Irradiation of halophosphate lamp phosphors by a low-pressure mercury arc causes a loss in luminescent efficiency, changes in the absorption spectra, and thermoluminescence. The 1849A wavelength is primarily responsible for these changes, which are partially reversed by longer wavelength radiation or by heat. X-radiation produces larger changes in the absorption spectra, which are compared to observations on unactivated halophosphates. The relation between luminescent efficiency and color center formation is discussed.The effect of ultraviolet radiation on phosphors is of considerable interest with respect to their stability in fluorescent lamps. The decrease in luminescent efficiency previously reported for several phosphors (1) was found to occur for the alkaline earth halophosphate phosphors. Production of color centers has been described resulting from u.v. and x-radiation of the luminescent (2, 3) and nonluminescent (4) forms of the halophosphates. The conditions which result in a decrease of luminescent efficiency and the formation of color centers have been examined further. These studies relate to the phosphors alone and are not directly applicable to operation in practical lamps where additional effects due to binders, gases, and the supporting glass may be of great importance.
Experiments and ResultsBoth commercially manufactured and laboratoryprepared halophosphate phosphors were studied. These have the general formula M5 (PO4)3 X: Sb, Mn where M is Ca and/or Sr; X is C1 and/or F; Sb is a sensitizer as well as an activator which produces a blue luminescence in the region of 4800A; and Mn is an activator which produces a peak in the 5800A region. Table I shows the qualitative composition of the phosphors studied. In addition, a sample of self-activated barium titanium phosphate was examined.
The system CdS-In2S3-Tm2S3 has been investigated with the objective of obtaining for physical studies semiconducting crystals with high rare earth content. The new compounds CdR2S4 and CdR2Se4, where R represents the rare earths of small ionic size, have been found to have the spinel structure. Thulium was chosen as representative of this group of rare earths, and studies have been made largely in the pseudobinary system CdIn2S4-CdTm2S4, in which complete solid solution was found to occur. Both powder samples and single crystals have been prepared, and their lattice constants and infrared fluorescence measured. The structure of CdTm2S4 has been shown to be of the normal spinel type. Weak infrared electroluminescence from single crystals has been observed.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 138.251.14.35
Five new ternary semiconducting compounds have been synthesized:
Cd4P2Cl3
,
Cd4P2Br3
,
Cd4P2I3
,
Cd4As2Br3
, and
Cd4A2I3
. These compounds are all cubic (space group Pa3) and isomorphous with each other. Their lattice constants vary with sizes of the component atoms. The structure appears to be based on a nearly face‐centered cubic arrangement of cadmium atoms in a pseudocell having half the edge of the true primitive cell. All the new compounds are deeply colored. Estimates of their energy band gaps have been made from optical and electrical measurements.
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